The fertilization of animals by artificial insemination (AI) and embryo transplant following in vitro fertilization is an established practice. In the livestock production industry, the ability to influence the reproductive outcome toward offspring having one or more desired characteristics has obvious advantages. By way of example, there would be an economic benefit in the dairy industry to preselect offspring in favor of the female sex to ensure the production of dairy cows. The separation of sperm into enriched populations of X and Y chromosome-bearing cells, known as gender enriched semen or gender enriched sperm, is one method of achieving preselected offspring.
In order to obtain gender enriched semen, sperm cells must be stained with a dye and subsequently sorted into X and Y chromosome-bearing cells. Each of staining and sorting processes places a stress on the sperm cells that decreases sperm cell viability or motility, particularly progressive motility.
Salisbury et al. describe a technique for the collection of ejaculated bovine semen directly into a diluent which inhibits cell motility and prevents the absorption of carbohydrates from the surrounding seminal plasma. When the ejaculate is collected into the diluent and the air phase above the liquid is replaced by gassing with 100% CO2, the cells in the ejaculate became immotile. As long as the cells remained in the diluent and air was excluded, the cells remained immotile for several hours at room temperature and for at least 8 days at 5° C.